This invention relates to teat cup assemblies for vacuum operated milking machines and, more particularly, to liners or inflations for teat cup assemblies of the type which are expanded at one end by insertion of an annular rigid expansion ring to form a diaphragm or mouthpiece including a central opening for receiving the teat of a cow.
The above type milking liner or inflation is usually formed from an elastomeric material, such as a natural or synthetic rubber composition. The teat-receiving end portion is expanded or stretched by the expansion ring through the useful life of the inflation. Repeated contact of the teat-receiving end portion of the inflation with rubber swelling substances on cows' teats, plus stretching when the mouthpiece opening is pushed sideways by a cow's teat, distorts the shape of the mouthpiece opening (out of round) so it no longer properly engages the teat. The misshapen hole permits undesirable amounts of air to enter the inflation during milking, resulting in excessive vacuum loss, slurping, inflation slippage and drop off.
Representative prior expansion ring type milking inflations designed to minimize fatigue during the use are disclosed in U.S. Pat. Nos. 2,120,556 (Greene), issued Aug. 20, 1936, 3,659,557 (Noorlander), issued May 2, 1972 and 4,116,165 (Arrington), issued Sept. 26, 1978. The Greene patent discloses an inflation including a bulbous enlargement for receiving the expansion ring. The Noorlander patent discloses forming the teat-receiving portion of the inflation with a plurality of longitudinally extending corrugations which cause the central opening to be undulated when an expansion ring is inserted. The Arrington patent discloses making the teat-receiving end portion tapered with the wall thickness decreasing along the taper.
Attention is also directed to U.S. Pat. Nos. 3,696,790 (Albright), issued Oct. 10, 1972, and 4,141,319 (Maier et al), issued Feb. 27, 1979. FIGS. 13 and 16 of the Albright patent illustrate an inflation having a teat-receiving portion including a plurality of radially extending corrugations and a circumferentially extending corrugation which respectively spread and squeeze when a teat is inserted into the central opening. FIGS. 4 and 5 of the Maier et al patent illustrate an inflation having a plurality of radially extending ribs which terminate short of the central opening and serve to support the radial tension applied on the edge of the central opening during use.
None of the above patents disclose an expansion ring type inflation arranged in a manner to isolate the mouthpiece opening from the effects of swelling which can cause distortion in the shape and size of the opening.